The invention relates to a method for routing data in communication networks and to a network node for routing data in communication networks.
It is known that in order to determine the path of a data packet, network nodes decide by which path a data packet is to be forwarded so that the latter reaches a receiving network node by, for example, the fastest possible path. This procedure is known as what is termed “routing”. Different approaches to implementing the routing culminated in different routing protocols.
According to routing protocols of this type, routes that have been determined are frequently associated with a “lifetime”, i.e. with a timeout, such that the routes are removed from routing tables in the event of non-acknowledgement of the route without additional control packets after a timer set with the lifetime has expired.
A similar approach is adopted in reactive routing protocols which are used for mobile so-called “ad hoc” networks, in particular wireless mesh networks, and which are based on the distance vector method, such as for example the so-called “Ad hoc On-Demand Distance Vector” (AODV) protocol (cf. Perkins, C. E., Belding-Royer, E. M., and Das, S. R. “Ad hoc On-Demand Distance Vector (AODV) routing”, IETF Experimental RFC 3561, July 2003, AODV RFC) or the “Hybrid Wireless Mesh Protocol” (HWMP) protocol (cf. IEEE P802.llsm/D0.03, Draft amendment to standard IEEE 802.11 TM: ESS Mesh Networking, IEEE, August 2006, Work in Progress).
Usually a route in a network is defined by corresponding entries in routing tables of network nodes. Every network node on the path from a source node to a destination node has in its routing table an entry for the destination node that specifies the next so-called “hop”, i.e. the next network node to be reached on the route to the destination node D.
In the case of the AODV and HWMP protocols, the reactive route search begins with a network-wide broadcast of what is termed a “route request” message (RREQ) which sets up what are termed “reverse routes” from all the network nodes to the source node. The destination node will also receive one or more RREQs. Every RREQ packet received stands for a possible route to the source node. On the selected reverse route the destination node sends a “route reply” message (RREP) by unicast, which message enters what is termed the “forward route” in all of the network nodes on the selected route.
A problem with this method of proceeding is that the lifetime of the reverse routes generated by the RREQs must be sufficiently long, since the reverse routes must also continue to exist when the RREP is sent back to the originator node S and S begins to send the data to D.